Currently, vehicles use heat from the engine as transmitted from the engine cooling system to the heater core located in the HVAC air handling system to warm the passenger compartment and defrost the windows. Current HVAC systems have a delay time in the production of heat to the passenger compartment. Additional sources of heat are desirable to augment the current vehicle HVAC system.
In vehicles with automatic temperature control (ATC) systems, it is desirable to utilize a supplemental heat system that fills the time delay between vehicle start up and ATC on-time, which is usually one to three minutes and controlled by or is a function of coolant temperature.
There have been various methods proposed for heat augmentation or supplementation to the HVAC system. For example, a first type of heat augmentation is a fuel fired pre-heater. The separate vehicle heating system consists of a heat exchanger, electrical control system, engine coolant water pump, vehicle fuel burner, and a fuel supply line is utilized.
A second type of heat augmentation includes electric heaters utilizing electric heating elements or coils as disclosed in U.S. Pat. No. 3,440,398 issued Apr. 22, 1969, in the name of Nilssen.
A third type of heat augmentation is a positive temperature coefficient (PTC) ceramic heater in series with the vehicle HVAC system. This contains two separate ceramic heat exchangers placed downstream of the heater core within the HVAC air handling system and a separate electrical control system. Modification to the vehicle's electrical system is required in order to supply the power to the system. An example of the ceramic heater is disclosed in U.S. Pat. No. 4,459,466 issued Jul. 10, 1984 in the name of Nakagawa et al.